Method and apparatus for supplying refrigerant fluid

ABSTRACT

An apparatus is disclosed for supplying a refrigerant fluid to a cooling device, such as a cryosurgical probe. An arrangement of valves may control the supply of fluid to and from the cooling device. Fluid may flow in a forward direction through the cooling device for generating cooling by expansion of the fluid in the cooling device. The apparatus may execute a programmed sequence of cooling and heating cycles automatically. Backflushing of the fluid may be used for clearing contaminants from the inlet side of the cooling device. A pulse width modulated control signal may be used to control one of the valves to have a variable effective aperture. A flow rate sensor may detect the flow rate through the cooling device. The detected flow rate may be used to detect an occurrence of a blockage and/or for controlling the fluid supplied to the cooling device. A blockage may be cleared by automatic backflushing.

FIELD OF THE INVENTION

The present invention may relate to supplying refrigerant fluid to, forexample, a cooling device for generating a cooling effect based onJoule-Thompson expansion of the fluid. The invention may be especiallyuseful in the field of medical or surgical use. The cooling device may,for example, be a cooling probe.

BACKGROUND TO THE INVENTION

The Joule-Thompson principle of isenthalpic expansion of certainrefrigerant fluids (e.g., gases) through a micro expansion orifice haslong been used in the medical field to create a freezing effect.Typically, the expansion orifice is located at the tip of a probethrough which the refrigerant fluid is driven under pressure. Theoperation of the probe is controlled by a fluid supply apparatusincluding one or more valves or regulators for controlling the flow offluid in the probe. A conventional fluid supply apparatus is described,for example, in WO 00/35362.

A significant problem is that the micro expansion orifice in the probeis vulnerable to blocking by foreign matter such as dust particles orother contaminants that may be contained in the refrigerant fluid orotherwise enter the probe. A blocked probe normally has to be returnedto a service center or factory for thorough cleaning before the probecan be used reliably again. For many cyro-surgeons and probe operators,the problem of probe blocking is considered to be a highly inconvenient,yet regular, occurrence that has to be tolerated as a result of thenature of the probe design.

Other problems remain in terms of difficulty of use of the fluid supplyapparatus and the probe, difficulty of handling fault conditions such asa blocked or faulty probe, and difficulty of reducing the risk ofoccurrence of probe blockage.

SUMMARY OF THE INVENTION

A first aspect of the present invention may be to provide an at leastmomentary backflushing of fluid through a cooling device. Thebackflushed fluid may be the same fluid as that used as the refrigerant.The backflushing may be effective to clear or dislodge any foreignmatter that may have been driven into an expansion orifice of thecooling device by the usual flow of fluid in the forward direction.

The backflushing may be controlled by an arrangement of valves. Thevalves may be configured in a first mode of operation in whichrefrigerant fluid may be caused to flow in a forward direction throughthe cooling device. The valves may further be configured in a secondmode of operation in which fluid may be caused to flow, at leastmomentarily, in a reverse direction through the cooling device. In oneform, the second mode may be a mode in which the cooling device may bepressurized such that pressure may develop in both an inlet side andoutlet side of the cooling device, whereafter the inlet side may bevented to cause pressurized fluid on the outlet side to backflushthrough the cooling device. Such a configuration may generate an abruptpressure differential or pressure wave that may be extremely effectiveto dislodge foreign matter blocking the cooling device.

The backflushing may be carried out when a blockage is detected in use.Additionally or alternatively, the backflushing may be carried outroutinely at intervals in use of the cooling device. For example, thebackflushing may be carried out following each freeze and/or thaw cycle(or each combined freeze-thaw cycle) of the cooling device. Suchfrequent backflushing has been found to be highly effective in reducingthe risk of occurrence of a blockage, even if the cooling device is usedmany times.

A second aspect of the invention may be to use, as a valve between ahigh pressure refrigerant fluid source, and an inlet side of a coolingdevice, a valve that is responsive to a pulse modulated electroniccontrol signal. The pulse modulated signal may be a pulse widthmodulated signal (PWM), or a pulse density modulated (PDM) signal. Apulsed valve may have a fast response, and be less expensive and yetmore reliable and durable than an equivalent servo driven valve.

A third aspect of the invention may be to implement an automatic gradualapplication of pressure to an inlet side of a cooling device, instead ofan abrupt application of refrigerant fluid at high pressure. Such agradual application of pressure may be referred to as a “soft start”.The gradual application of pressure may help reduce the risk of blockagein the cooling device by avoiding an abrupt pressure wave in the forwarddirection through the cooling device that may otherwise force foreignmatter on the inlet side of the cooling device into the expansionorifice.

A fourth aspect of the invention may be for a control unit of the fluidsupply apparatus to be provided with one or more program sequences eachof one or more freeze-thaw cycles. The control unit may be responsive toa manual start command from an operator to begin performing a selectedprogram sequence. Thereafter, the control unit may be configured toautomatically advance through the program sequence without any furtherinput from the operator. The control unit may be responsive to aninterrupt command from the operator to enable the program sequence to behalted at any moment if desired by the operator.

A fifth aspect of the invention may be to measure the flow rate ofrefrigerant fluid passing through the cooling device, at least in one ormore certain modes of operation of the cooling device. A flow ratesensor may be coupled to a low pressure side of the cooling device.Coupling the flow rate sensor on the low pressure side may enable a lessexpensive flow rate sensor to be used.

The measured flow rate may be used to detect the occurrence of ablockage in the cooling device. For example, a blockage may beidentified when the flow rate is zero or unusually small. In response toa detected blockage, a warning signal may be generated. Additionally oralternatively, a self-unblocking operation may be initiated to try toclear the blockage. The self-unblocking operation may includebackflushing fluid through the cooling device in an opposite directionto the normal flow during cooling.

The measured flow rate may also, or alternatively, be used incombination with a measured fluid pressure and/or temperature, in afeedback loop for regulating the fluid pressure applied to the coolingdevice in order to control the performance of the cooling device.

Other features, objects and advantages of the invention may be definedin the claims and/or apparent from the following description of apreferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting preferred embodiment of the invention is now described byway of example with reference to the claims and accompanying drawings inwhich:

FIG. 1 is a schematic diagram of fluid and control circuitry for arefrigerant fluid supply apparatus;

FIG. 2 is a schematic flow diagram illustrating operating modes of thefluid supply apparatus;

FIGS. 3-6 are schematic flow diagram illustrating details of FIG. 2;

FIGS. 7 and 8 are schematic representations of preset freeze-thawprograms;

FIG. 9 is a schematic flow diagram illustrating performance of apredefined sequence of free-thaw cycles; and

FIGS. 10(a)-(c) are schematic representations of a valve control signaluseable in the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 may generally illustrate a fluid supply apparatus 10 forsupplying and controlling the flow of a refrigerant fluid to a coolingdevice 12. The cooling device 12 may be detachably connectible to acoupling 18 of the apparatus 10. The cooling device 12 may be a medicalor surgical probe. The cooling device 12 may include a small orifice(depicted schematically at 14) for generating a freezing effect by theJoule-Thompson principle of isenthalpic expansion when fluid is forcedthrough the orifice 14 from an inlet side 12 a to an outlet side 12 b.The terms “inlet side” and “outlet side” may refer to a normal directionof fluid flow through the cooling device 12 for generating the intendedfreezing effect. The refrigerant fluid may be any suitable fluid forgenerating significant cooling upon isenthalpic expansion. Such a fluidmay often be referred to as a Joule-Thompson fluid and may be a gas. Forexample, the gas may be nitrous oxide.

The supply apparatus 10 may generally comprise a first arrangement ofvalves V1-V4 for controlling a flow of the refrigerant fluid through(e.g. to and/or from) the cooling device 12, and a second arrangement ofvalves V5-V8 for selecting an active one of a plurality of sources 15a-d of the refrigerant fluid to supply to a fluid supply node 16 in theapparatus. The normal fluid pressure from the active source 15 a-d atthe fluid supply node 16 may typically be between 650 and 900 psi.

In more detail, a first valve (or “freeze valve”) V1 may be coupledbetween the fluid supply node 16 and a first coupling port (e.g., firstcoupling conduit) 18 a to the inlet side 12 a of the cooling device 12.The first valve V1 may supply fluid to the coupling port 18 a. A secondvalve (or “purge valve”) V2 may be coupled between the fluid supply node16 and a second coupling port 18 b (e.g., second coupling conduit) tothe outlet side 12 b of the cooling device 12. The second valve V2 maysupply fluid to the second coupling port 18 b. A pressure reducingresistance or constriction or shunt 20 may be coupled in series with thesecond valve V2 for reducing the pressure in response to fluid flowthrough the second valve V2. The first and second valves V1 and V2 maycollectively be referred to as “supply valves” for deliveringpressurized fluid to the inlet and outlet sides 12 a, and 12 b, of thecooling device 12.

A third valve (or “inlet vent valve”) V3 may be coupled between thefirst coupling port 18 a and an exhaust port 22 for venting spent fluidfrom the apparatus. The third valve V3 may selectively vent the firstcoupling port 18 a independently of the second coupling port 18 b. Afourth valve (or “exhaust vent valve”) V4 may be coupled between thesecond coupling port 18 b and the exhaust port 22. The fourth valve V4may selectively vent the second coupling port 18 b independently of thefirst coupling port 18 a. Although a single exhaust port 22 may beillustrated, the third and fourth valves V3 and V4 may alternatively becoupled to different exhaust ports or vents. A flow rate sensor F may becoupled in series with the fourth valve V4 for measuring the flowthrough the fourth valve V4. The flow rate sensor may be coupled via thefourth valve V4 to the second coupling port 18 b, which may be referredto as a low pressure side of the cooling device 12. The flow rate sensorF may be coupled between the exhaust port 22 and the fourth valve V4 sothat the fourth valve V4 may be used to isolate the flow rate sensor Ffrom an excessive pressure. A parallel shunt 24 may be coupled inparallel with the flow rate sensor F, for enabling the flow rate sensorF to be used to sense a higher flow rate than the through-flow capacityof the flow rate sensor F alone. The flow rate sensor F may enable theflow of fluid through the cooling device 12 to be monitored, so that anyoccurrence of a blockage may be detected. The third and fourth valves V3and V4 may collectively be referred to as “vent valves” for venting theinlet and outlet sides 12 a and 12 b of the cooling device 12.

The first and second valves V1 and V2 may be normally-closed valves. Thethird and fourth valves V3 and V4 may be normally-open valves. Such anarrangement may provide a fail-safe mode, should any of the valves fail.The first and second valves V1 and V2 may fail-safe closed, such thatrefrigerant fluid is shut off by each valve. The third and fourth valvesV3 and V4 may fail-safe open, such that the any fluid pressure in thecooling device 12 may be vented through the exhaust port 22.

An electronic control unit 26 may generate respective control signalsVCS1, VCS2, VCS3 and VCS4 for controlling the valves V1-V4. Theelectronic control unit 26 may receive a flow rate signal FS generatedby the flow rate sensor F. The electronic control unit 26 may alsoreceive first and second pressure signals PS1 and PS2 from first andsecond fluid pressure sensors P1 and P2. The first pressure sensor P1may be coupled to sense the fluid pressure at the fluid supply node 16.The first pressure signal PS1 may provide a direct indication of thefluid supply pressure from the active supply source, as described later.The second pressure sensor P2 may be coupled to sense the fluid pressureat the first coupling port 18 a. The second pressure signal PS2 mayprovide an indication of the pressure applied to the cooling device 12in normal use, and may also be used to pressure-test the cooling device12 to detect leaks, as described later.

The electronic control unit 26 may further receive one or more inputand/or command signals from a remote control device 28. The remotecontrol device may, for example, be a foot switch. An advantage of afoot switch is that an operator may control the apparatus 10 withoutcontaminating his or her hands, if the operator requires sterileconditions to be maintained. The electronic control unit 26 may furtherreceive one or more input and/or command signals from input switches 30mounted on a control panel of the apparatus 10. The electronic controlunit 26 may further receive a temperature signal from a temperaturesensor (not shown) if such a temperature sensor is provided in thecooling device 12.

Referring to FIG. 2, the control unit 26 may control the apparatus 10 inone or more operation modes. The modes may include rest mode 31, apressure test mode 32, a purge mode 34, a freeze or cooling mode 36, athaw or heating mode 38, a backflush mode 40 and/or an unblock mode 59.The rest mode 31 may correspond to the fail-safe condition of the firstto fourth valves V1-V4. The operation cycles of the apparatus 10 maybegin and/or end (e.g., loop back to) the rest mode 31.

When a cooling device 12 may be connected to the coupling 18, thecontrol unit 26 may firstly initiate the test mode 32 to test whetherthe cooling device is adequately pressure tight. Referring to FIG. 3, atstep 42 the first to fourth valves V1-V4 may all set to their closedcondition. At step 44, the first valve V1 and/or the second valve V2 maybe opened to pressurize the cooling device 12 from the fluid supply node16. The cooling device may be pressurized to the full pressure of thefluid supply node 16. The first valve V1 and/or second valve V2 may beheld open for a predetermined period of time, or until the pressuremeasured by the second pressure sensor P2 may have stabilized. At step46, the pressure measured by the second pressure sensor P2 may berecorded, and the first valve V1 and/or second valve V2 may again beclosed, so that the cooling device 12 is again isolated, but in apressurized state. At step 48, after a predetermined test duration, thepressure measured by the second pressure sensor P2 may again berecorded, and compared with the previously recorded value. When the twopressure values are the same (or differ by less than a certain allowabletolerance), the cooling device 12 may be considered to be adequatelypressure tight, and acceptable for use. When the two pressure values arenot the same (or differ by more than the allowable tolerance), thecooling device 12 may be considered to be leaky. In the case of a leakydevice, the control unit 26 may inhibit any further operation with thatcooling device 12. A leaky device may be potentially unsafe. Forexample, there may be risk that leaked refrigerant fluid may enter apatient's blood stream should the cooling device be used on a patient,or there may be risk of the cooling device 12 losing structuralintegrity.

After step 48, the pressure in the cooling device 12 may be vented atstep 50 by opening the third valve V3 and/or the fourth valve V4. Thethird valve V3 may be opened before the fourth valve V4 in order toallow most of the pressure to vent through the third valve V3 before thefourth valve V4 is opened. Opening the third valve V3 before the fourthvalve V4 may protect the flow rate sensor F from an excessive flow rateoutside its normal range. Opening the third valve V3 before the fourthvalve V4 may also generate an at least momentary backflushing of highpressure fluid through the cooling device 12 (for example, fluid underpressure on the outlet side 12 b may flow in a reverse direction throughthe orifice 14 to vent via the inlet side 12 a). Such high pressureand/or abrupt backflushing of fluid has been found to be extremelyuseful to clear any foreign matter at least from the vicinity of theorifice 14 of the cooling device 12, and hence reduce the risk ofblockage at the orifice 14.

When the cooling device 12 may have successfully passed the pressuretest 32, the operation may loop back to the rest mode 31 before thepurge mode 34 is invoked, or may proceed immediately to a purge mode 34.The purge mode 34 may be effective to remove accumulated moisture fromthe cooling device 12. Referring to FIG. 4, at step 52, all of the firstto fourth valves V1-V4 may initially be set closed. At step 54, thesecond valve V2 and the third valve V3 may be opened, to create a flowof fluid from the fluid supply node 16 via the second valve V2 and thepressure reducing shunt 20 to the outlet side 12 b of the cooling device12. The flow of fluid may be vented from the inlet side 12 a of thecooling device, through the third valve V3 to the exhaust port 22. Inthe purge mode 34, the pressure of the fluid may be reduced to a modestlevel by the effect of the pressure reducing shunt 20 while fluid isflowing. The modest pressure level may, for example be less than 300psi, or less than 250 psi. The flow may be maintained for apredetermined period of time effective to purge moisture from theapparatus 10 and the cooling device 12. At the end of the purge mode,the flow of fluid may be halted at step 56 by closing the second valveV2. The fourth valve V4 may be opened at step 58 to vent any residualpressure on the outlet side 12 b of the cooling device 12.

Following the purge mode 34, the operation may return to the rest mode31 awaiting a command to begin a freeze-thaw operation. In a freeze-thawoperation, the control unit 26 may initiate one or more cycles of thefreeze mode 36, thaw mode 38 and backflush mode 40. The cycle may, forexample, be initiated in response to a command from the remote controlunit 28. Referring to FIG. 5, the freeze mode 36 may be entered at step60 by setting the second and third valves V2 and V3 shut, and by openingthe first and fourth valves V1 and V4. Fluid at high pressure may flowfrom the fluid supply node 16 via the first valve V1 to the inlet side12 a of the cooling device 12. The high pressure fluid may flow in theforward direction through the orifice 14, creating cooling by theJoule-Thomson effect. The expanded fluid may vent from the outlet side12 d of the cooling device via the fourth valve V4 and the flow ratesensor F to the exhaust port 22. The second pressure sensor P2 and theflow rate sensor F may provide useful indications of the state of thefluid flow and/or operation of the cooling device 12. In particular, theflow rate signal FS from the flow rate sensor F may provide a directindication of whether fluid is flowing freely through the cooling device12, or whether flow may be restricted or completely stopped, forexample, by a blockage in the cooling device 12. When a blockage isdetected, then the control unit 26 may invoke the unblock mode 51(described below) to try to clear the blockage.

The duration of the freeze mode 36 may be predetermined by a presetprogram within the control unit 26, or it may be controlled manually byan operator, for example, by using the remote control device 28. At theend of the freeze mode 36, operation may proceed to the thaw mode 38. Atstep 62, the fourth valve V4 may be closed to halt the venting of fluidfrom the outlet side 12 b of the cooling device 12 through the exhaustport 22. A thaw or defrost effect may be generated in the cooling device12 by progressive re-pressurization of the fluid trapped on the outletside 12 b of the cooling device 12. As an optional step 64, the secondvalve V2 may be opened to increase the rate of pressurization of theoutlet side 12 b, and hence generate a more rapid thaw effect. Theduration of the thaw mode 38 may be predetermined by a preset programwithin the control unit 26, or controlled manually by the operator (forexample, using the remote control device 28).

Following the thaw mode 38, operation may proceed to the backflush mode40. At step 66, the cooling device 12 may be isolated from the fluidsupply node 16, but kept in the pressurized state. For example, at step66, the first valve V1 may be closed to halt the supply of refrigerantfluid to the inlet side 12 a of the cooling device 12. If at step 64 thesecond valve V2 may have been opened during the thaw mode 38, the secondvalve V2 may also be re-closed at step 66. At step 68, the third valveV3 may be opened to allow the trapped fluid to vent from the inlet side12 a of the cooling device 12. In a similar manner to step 50 describedabove, opening the third valve V3 may generate an at least momentarybackflushing of fluid through the orifice 14, which has been found to beextremely effective for reducing the risk of blockage at the orifice 14.The backflush mode 40 may be used at the end of each freeze-thaw cycle.Such regular high-pressure backflushing can extend the usability of thecooling device 12 considerably compared to a conventional fluid supplyapparatus which does not provide the same backflush operation. Inparticular, the cooling device 12 may be used numerous times withoutblocking, in contrast to the high risk of blocking when a cooling deviceis driven by a conventional gas supply apparatus.

After the backflush mode 40, operation may loop back to the freeze mode36 if, for example, a sequence of multiple freeze-thaw cycles may beused as part of the same treatment. A sequence of multiple freeze-thawcycles may be controlled automatically be the control unit 26, ormanually, for example, using the remote control device 28. Aftercompletion of the freeze-thaw cycles, the control unit 26 may return theapparatus to the rest mode 31.

As mentioned above, when a blockage is detected during the freeze mode36, operation may branch to the unblock mode 59. The operation of theunblock mode 59 may be similar to the backflushing described previouslyfor steps 50 and 68. Referring to FIG. 6, at step 70, the cooling device12 may be pressurized to a high pressure, by opening the first valve V1and/or the second valve V2 while closing the third valve V3 and thefourth valve V4. Then, at step 72, the fluid may be backflushed throughthe orifice 14 by opening the third valve V3 while closing at least thefirst valve V1. The second valve V2 may remain open or closed duringbackflushing. The fourth valve V4 may remain closed during thebackflushing, to avoid any pressure loss on the outlet side 12 b of thecooling device 12. After backflushing, the fourth valve V4 may be openedat step 74 to vent any residual pressure on the outlet side 12 b. Duringstep 74, the flow rate measured by the flow rate sensor F may bemonitored to detect whether a significant amount of fluid may ventthrough the fourth valve V4. If the blockage has been cleared, then verylittle fluid may vent through the fourth valve V4. A large quantity offluid venting through V4 may indicate that the blockage may not havebeen cleared. One or more backflush cycles may be performed in sequenceto try to clear a blockage of the cooling device. Following the unblockmode 59, operation may return to the freeze mode 36. Alternatively, thecontrol unit 26 may signal a warning or a report to the operator toindicate that a probe blockage has occurred, and/or to indicate whetheror not the blockage has been cleared.

In the foregoing description, backflushing may be achieved bypressurising both the inlet side 12 a and the outlet side 12 b of thecooling device 12, and opening the third valve V3 to vent the fluid fromthe inlet side 12 a. Opening the third valve V3 while keeping the fourthvalve V4 closed may generate an at least momentary flow of a quantity ofpressurized fluid from the outlet side 12 b through the orifice 14 tothe inlet side 12 a, thereby backflushing fluid through the orifice. Thebackflushing may generate an abrupt pressure burst or pressure waveacross the orifice, which is extremely effective in clearing foreignmatter from the orifice 14. The magnitude of a backflush pressuredifferential across the orifice may be at least, or greater than, anyof: 300 psi, 350 psi, 400 psi, 450 psi, 500 psi, 550 psi, 600 psi, 650psi, 700 psi, 750 psi, 800 psi, or 850 psi. As an alternative to amomentary flow, a separate back-flush valve V9 may be coupled from thefluid supply node 16 to the second coupling port 18 b. The back flushvalve V9 may be operated to provide a continuous flow of high pressurefluid to the outlet side 12 b of the cooling device, for continuousbackflushing through the orifice 14.

Referring to FIG. 1, the control unit 26 may comprise a storage device80 for storing one or more program sequences of freeze-thaw cycles. Thestorage device 80 may be a non-volatile storage device. The storagedevice may, for example, comprise a non-volatile semiconductor memory,or magnetic or optical media. The program sequences may be programmableby the operator, or predefined within the control unit 26. FIG. 7 mayillustrate a first example format for storing the one or more programsequences 82 a, 82 b. Referring to FIG. 7, each program sequence 82 a,82 b may include data representing at least durations 84 of a sequenceof freeze modes 36 and thaw modes 38. The durations 84 may includefreeze mode durations 84 a and thaw mode durations 84 b. In the firstexample format, separate data may be provided for each mode in theprogram sequence 82. Providing separate data may enable the duration offreezing and thawing to be varied at different parts of the sequence.For example, the first sequence 82 a may define a first freeze cycle of3 minutes, a second thaw cycle of 30 seconds, a third freeze cycle of 2minutes, and a fourth thaw cycle of 20 seconds. The second sequence 82 bmay define a first freeze cycle of 3 minutes, a second thaw cycle of 30seconds, a third freeze cycle of 3 minutes and a fourth freeze cycle of30 seconds.

FIG. 8 may illustrate a second example format for storing one of moreprogram sequences 86 a, 86 b in a special case in which the durations ofthe freeze modes 36 and thaw modes 38 may not vary throughout theprogram sequence. Referring to FIG. 8, each program sequence 86 a, 86 bmay comprise data representing at least a duration 88 a of a singlefreeze mode 36, a duration of a single thaw mode 38, and a number 88 cof repetitions of the free-thaw cycles in the program sequence. Forexample, a first sequence 86 a may define 2 repetition of cycles of a 3minute freeze and a 30 second thaw. The first sequence 86 a may be thesame as the sequence 82 b described with respect to FIG. 7. A secondsequence may define 3 repetition cycles of a 3 minute freeze and a 30second thaw.

The number of program sequences 82 or 86 may depend on a specificapplication for which the apparatus 10 is intended. For example, only asingle program sequence 82 or 86 may be provided in some applications.An operator may select the single program sequence 82 or 86, or mayselect between plural program sequences 82 or 86, using the selectors30. Referring to FIG. 9, once a program sequence has been selected, atstep 90 the control unit 26 may be responsive to a “start” command froman operator. The “start” command may be inputted through one of theinput switches 30 or through the remote control device 28. Once the“start” command has been received, operation may proceed to step 92 atwhich the selected program sequence may be retrieved from the storagedevice 80 and the defined freeze-thaw cycles of the program sequence maybe performed. For example, the sequence of freeze-thaw cycles may beperformed one after the other without any further inputs from theoperator. During step 92, the control unit 26 may be responsive to aninterrupt signal from the operator for halting the program sequence. Theinterrupt signal may be inputted through the input switches 30 orthrough the remote control device 28. When the interrupt signal isreceived, operation may proceed to step 94 at which the program sequencemay be halted. For example, the first and second valves V1 and V2 may beclosed, and the third and fourth valves V3 and V4 opened. The thirdvalve V3 may be opened before the fourth valve V4, in order to protectthe flow rate sensor F, in a similar manner to that described for step50. Alternatively, at step 94, the thaw mode 38 may be invoked in orderto immediately reverse any freezing at the cooling device 12. Theautomatic performance of a program sequence may enable the operation ofthe cooling device 12 and the supply apparatus 10 to be simplified, andenable surgeons not familiar with manually operation to use theapparatus 10 with ease. Moreover, when the remote control device 12 maybe used to provide the start command and/or the interrupt command, theoperator need not contaminate his or her hands if sterile conditions arepreferred. This may enable a procedure to be carried out by a singleperson, rather than involving one person to hold and position thecooling device (in sterile conditions) and another person to manipulatethe controls of the refrigerant supply apparatus.

Referring again to FIG. 1, each of the fluid supply sources 15 a-d maycomprise a replaceable fluid cylinder. The cylinders may be mountablewithin the apparatus 10. Each source 15 a-d may be coupled via anon-return valve 100 a-d and a filter 102 a-d to a respective one offifth, sixth, seventh and eighth valves V5-V8, respectively. The fifthto eighth valves V5-V8 may be coupled to the fluid supply node 16 toenable fluid to be drawn from a selected one of the sources 15 a-d, andfed to the fluid supply node 16. A function of the filters 102 a-d maybe to remove at least some dust particles or other foreign matter fromthe supplied fluid, in order to reduce the risk of blockage of thecooling device 12. The control unit 26 may be responsive to the pressuremeasured by the first pressure sensor P1 to determine the state of acurrently selected one of the sources 15 a-d. When the pressure may dropbelow a predetermined threshold indicative of the source 15 a-d runningnearly empty, the control unit 26 may operate respective valves of thefifth to eighth valves V5-V8 to automatically decouple the depletedsource, and to select instead another source. Such automatic operationmay be performed while fluid is being supplied to the cooling device 12,so that the operation of the cooling device 12 may not be interrupted.

The components within the broken line 104 of FIG. 1 may conveniently bemounted on an integral manifold unit (not shown) having conduit boresand chambers for forming the fluid flow paths indicated in FIG. 1.

The first to eighth (or ninth) valves V1-V8 (and V9) may be electricallyoperated valves. The valves may, for example, be solenoid operatedvalves. The first valve V1 may be configured to have a variableaperture, to provide a variable flow control between a fully opencondition and a fully closed condition. For example, the first valve V1may be a variable servo controlled valve. Alternatively, the first valveV1 may be of a type intended to be driven by a modulated signal forcontrolling the first valve V1 according to a degree of modulation. Forexample, referring to FIG. 10, the first control signal VCS1 may be apulse modulated signal. The pulse modulated signal may be a pulse widthmodulated (PWM) signal. The degree of opening of the first valve V1 maybe controlled by a duty ratio of the PWM signal. FIG. 10 a mayillustrate a first example of the control signal VCS1 having a high dutyratio of on-time:off-time, for controlling the first valve V1 to have alarge aperture (e.g., almost completely open). FIG. 10 b may illustratea second example of the control signal VCS1 having an approximately 50%duty ratio of on-time:off-time, for controlling the first valve V1 tohave a medium aperture (e.g. approximately half-way open). FIG. 10 c mayillustrate a third example of the control signal VCS1 having a smallduty ratio of on-time:off-time, for controlling the first valve V1 tohave a small aperture (e.g., almost closed). The control unit 26 maycontrol the duty ratio of the first control signal VCS1 to besubstantially continuously variable, or to have a predetermined numberof quantized values. The frequency of the first control signal VCS1 maybe between 100 Hz and 1000 Hz. Depending on the frequency, a shutter(not shown) of the first valve V1 may either physically oscillatebetween the fully open and closed states in accordance with each pulseof the control signal VCS1, or the shutter may effectively hover betweenthe fully open and closed states, at a mean position determined by theduty ratio of the control signal VCS1. A pulsed valve may be any of lessexpensive, more reliable, and/or more durable than an equivalent servodriven valve.

Variable flow control of the first valve V1 (either by using a pulsedvalve or a servo driven valve) may provide additional advantages. Agradual start (or “soft start”) of the freeze cycle 36 may be effectedby gradually increasing the fluid pressure applied at the inlet side 12a of the cooling device, instead of abruptly applying full pressure tothe inlet side 12 a in the forward direction. A gradual increase inpressure may reduce the risk of blockage at the orifice 14 by avoidingan abrupt pressure wave that could force dust or other foreign matter onthe inlet side 12 a to be driven into the orifice 14.

Furthermore, the control unit 26 may be configured to determine anoptimum state of the first valve V1 that may optimise the use of therefrigerant fluid. The control unit 26 may be responsive to the signalsfrom the second pressure sensor P2 and the flow rate sensor F to controlthe first valve V1. For example, the fluid use may be optimised toachieve a flow rate that produces an adequate cooling effect whileconsuming fluid efficiently. Alternatively, the fluid use may beoptimised to achieve a maximum cooling effect.

A further advantage of a variable flow of the first valve V1 may thatthe first valve V1 may be controlled to provide a modest pressure levelof refrigerant fluid, for performing a purge in a forward directionthrough the cooling device 12. For example, a forward purge may beperformed by closing the second and third valves V2 and V3, opening thefourth valve V4, and opening the first valve V1 partly. The first valveV1 may supply modest pressure fluid to the inlet side 12 a of thecooling device, and the fluid may vent from the outlet side 12 b of thecooling device via the fourth valve V4 and the flow rate sensor F to theexhaust port 22. A modest pressure may not generate significant coolingwithin the cooling device 12, and so the forward purge may not generatenoticeable or undesirable cooling. The flow rate sensor F may be used tomonitor the state of flow of the fluid, and to detect an occurrence of ablockage at the orifice 14. Should a blockage be detected, then theunblock mode 59 may be invoked to try to clear the blockage before thecooling device 12 may be used.

Although variable flow control of the first valve V1 may be preferred,in an alternative form the first valve V1 may be a straightforwardopen-closed valve, similar to the other valves V2-V8.

It will be appreciated that the present invention, especially asdescribed in the preferred embodiment, may provide significantadvantages in terms of reducing blockage of a cooling device, and/orautomatically unblocking a blocked cooling device, and/or automaticallydetecting fault conditions, and/or simplifying operation of the coolingdevice.

An apparatus may be disclosed herein for supplying a refrigerant fluidto a cooling device, such as a cryosurgical probe. The apparatus mayinclude any or all of the following features: An arrangement of valvesmay control the supply of fluid to and from the cooling device. Fluidmay flow in a forward direction through the cooling device forgenerating cooling by expansion of the fluid in the cooling device. Theapparatus may execute a programmed sequence of cooling and heatingcycles automatically. Backflushing of the fluid may be used for clearingcontaminants from the inlet side of the cooling device. A pulse widthmodulated control signal may be used to control one of the valves tohave a variable effective aperture. A flow rate sensor may detect theflow rate through the cooling device. The detected flow rate may be usedto detect an occurrence of a blockage and/or for controlling the fluidsupplied to the cooling device. A blockage may be cleared by automaticbackflushing.

Although certain features of significance may have been defined hereinand/or in the appended claims, the Applicant claims protection for anynovel feature of combination of features described herein and/orillustrated in the drawings whether or not emphasis has been placedthereon.

1. Apparatus for supplying refrigerant fluid to a cooling device, saidapparatus comprising: an arrangement of valves for controlling fluidflow to and from said cooling device; and a control unit configured tocontrol said arrangement of valves in: (i) a first operating mode inwhich said refrigerant fluid flows in a first direction through saidcooling device for generating a cooling effect in said cooling device;and (ii) a second operating mode in which said refrigerant fluid flowsat least momentarily in an opposite second direction through saidcooling device for backflushing said cooling device.
 2. The apparatus ofclaim 1, wherein in said second mode, an at least momentary pressuredifferential is created across said cooling device to cause saidrefrigerant fluid to flow in said second direction.
 3. The apparatus ofclaim 2, wherein said pressure differential is greater than 300 psi. 4.The apparatus of claim 2, further comprising first and second fluidconduits for communicating with said coupling device, and wherein saidcontrol unit is configured in said second operating mode to control saidarrangement of valves to create a head of pressure directly orindirectly in at least said second conduit, and to vent pressure fromsaid first conduit during or after creating said head of pressure. 5.The apparatus of claim 4, wherein said control unit is furtherconfigured to control the arrangement of valves in said first operatingmode to supply refrigerant fluid to said first conduit and to vent fluidfrom said second conduit.
 6. The apparatus of claim 4, wherein saidcontrol unit is configured to control said arrangement of valves to ventsaid first conduit after creating said head of pressure, and whereinsaid head of pressure is created in said second conduit by a thirdoperating mode of supplying said refrigerant fluid through said firstconduit and said cooling device to said second conduit, and blockingventing of fluid from said second conduit.
 7. The apparatus of claim 6,wherein said third operating mode is a thaw mode for heating saidcooling device following a cooling operation.
 8. The apparatus of claim1, wherein said first operating mode is a cooling mode of said coolingdevice, and wherein said second operating mode is a post-cooling modesubsequent to said cooling mode.
 9. The apparatus of claim 2, whereinsaid control unit is configured to perform said second operating modeafter each performance of said first operating mode as part of acombined cycle.
 10. Apparatus for supplying refrigerant fluid to acooling device, said apparatus comprising: a first valve for controllingfluid flow to said cooling device; and a control unit configured togenerate a pulse modulated control signal for controlling said firstvalve, wherein said pulse modulated signal is effective to control saidfirst valve in a partly open condition.
 11. The apparatus of claim 10,wherein said pulse modulated control signal is a pulse width modulatedsignal.
 12. The apparatus of claim 11, wherein said first valve isconfigured to open to an extent responsive to a duty ratio of said pulsewidth modulated signal.
 13. Apparatus for supplying refrigerant fluid toa cooling device, said apparatus comprising: a first valve forcontrolling fluid flow to said cooling device; and a control unitconfigured to generate a control signal for controlling an extent ofopening of said first valve, wherein said control unit is configured, inresponse to a command to open said first valve, to generate said controlsignal to open said valve gradually over an interval of time, whereby apressure of said refrigerant gas supplied to said cooling deviceincreases gradually.
 14. The apparatus of claim 13, wherein said controlsignal is a pulse modulated signal.
 15. Apparatus for supplyingrefrigerant fluid to a cooling device, said apparatus comprising: anarrangement of valves for controlling fluid flow to and from saidcooling device; and a control unit configured to control saidarrangement of valves in at least a first mode of operation forgenerating cooling in said cooling device, and a second mode ofoperation for generating heating in said cooling device; said controldevice comprising a storage device for storing data defining a programsequence of at least one cycle of said first and second modes, and saidcontrol unit being configured to execute said program sequence.
 16. Theapparatus of claim 15, further comprising an input device for inputtinga command to said control unit, wherein said control unit is responsiveto said command to begin execution of said program sequence.
 17. Theapparatus of claim 16, wherein said input device comprises afoot-switch.
 18. The apparatus of claim 15, wherein said storage deviceis configured to store a plurality of selectable program sequences. 19.Apparatus for supplying refrigerant fluid to a cooling device, saidapparatus comprising: an arrangement of valves for controlling a flow ofsaid refrigerant fluid to and from said cooling device; a flow ratesensor for sensing a flow rate of said refrigerant fluid and forgenerating a flow rate signal; and a control unit responsive to saidflow rate signal and configured to control said arrangement of valves.20. The apparatus of claim 19, wherein said flow rate sensor is coupledto a low pressure side of said cooling device.
 21. The apparatus ofclaim 19, wherein said control unit is configured to detect anoccurrence of a blockage in said cooling device when said flow ratesignal indicates an abnormally small flow rate of said refrigerantfluid.
 22. The apparatus of claim 21, wherein said control unit isconfigured to perform an unblocking operation in response to detectionof a blockage.
 23. The apparatus of claim 22, wherein said unblockingoperation is a backflush of said refrigerant fluid through said coolingdevice.
 24. The apparatus of claim 19, wherein said control unit isconfigured to adjust a pressure of said refrigerant fluid supplied tosaid cooling device in response to the flow rate signal.
 25. Apparatusfor supplying a refrigerant fluid to a cooling device, the apparatuscomprising: a fluid supply conduit for receiving refrigerant fluid froma supply source; first and second coupling conduits for communicatingwith said cooling device; a first valve coupled between said fluidsupply conduit and said first coupling conduit for selectively applyingfluid pressure to said first coupling conduit; a second valve coupledbetween said fluid supply conduit said second conduit for selectivelyapplying fluid pressure to said second coupling conduit; a third valvecoupled between said first coupling conduit and a vent for selectivelyventing said first coupling conduit independently of said secondcoupling conduit; a fourth valve coupled between said second couplingconduit and a vent for selectively venting said second coupling conduitindependently of said first coupling conduit.
 26. The apparatus of claim25, further comprising a flow resistance coupled in series with saidsecond valve between said fluid supply conduit and said second conduit.27. The apparatus of claim 25, further comprising a flow rate sensorcoupled in series with the fourth valve between said second couplingconduit and said vent.
 28. The apparatus of claim 27, wherein said flowrate sensor is coupled between said fourth valve and said vent.
 29. Theapparatus of claim 25, wherein said apparatus is configured to operatein a cooling mode for supplying refrigerant fluid in a forward directionthrough said cooling device, wherein said first valve and said fourthvalve are open, and said second valve and said third valve are closed.30. The apparatus of claim 25, wherein said apparatus is configured tooperate in a heating mode in which a head of pressure is createddirectly or indirectly in each of said first and second supply conduits,wherein at least one of said first and second valves is open, and saidthird valve and said fourth valve are closed.
 31. The apparatus of claim25, wherein said apparatus is configured to operate in a backflushingmode in which a head of pressure is backflushed from said second conduitthrough said cooling device to said first conduit, wherein said firstvalve and said fourth valve are closed, and said third valve is open.32. The apparatus of claim 25, wherein said first and second valves arenormally closed valves, and said third and fourth valves are normallyopen valves.
 33. A method of operation of an apparatus for supplyingrefrigerant fluid to a cooling device, the method comprising:controlling an arrangement of valves for controlling fluid flow to andfrom said cooling device, in: (i) a first operating mode in which saidrefrigerant fluid flows in a first direction through said cooling devicefor generating a cooling effect in said cooling device; and (ii) asecond operating mode in which said refrigerant fluid flows at leastmomentarily in an opposite second direction through said cooling devicefor backflushing said cooling device.
 34. A method of operation of anapparatus for supplying fluid refrigerant to a cooling device, themethod comprising: generating a pulse modulated command signalindicative of a commanded extent of valve opening; and applying saidpulse modulated command signal to a first valve configured forcontrolling refrigerant fluid flow to said cooling device, to open saidvalve to said commanded extent.
 35. A method of operation of anapparatus for supplying refrigerant fluid to a cooling device, themethod comprising: providing data representing a programmed sequence ofoperating modes of said apparatus, said operating modes including acooling mode and a heating mode; and executing said program sequenceautomatically by advancing from one mode to a next mode in a mannerdefined by the programmed sequence.
 36. A method of operation of anapparatus for supplying fluid refrigerant to a cooling device, themethod comprising: sensing a flow rate of said refrigerant fluid; andcontrolling, in response to said sensed flow rate, an arrangement ofvalves configured to control fluid flow to and from said cooling device.